Precision Bearings: Precision Grade and Tolerance

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One of the factors you will definitely want to take into account when purchasing ball bearings is the issue of precision. There are two types of precision for Ball Bearings. One is dimensional accuracy and the other is rotational accuracy.
Dimensional accuracy for bearings is a measure of the error between the actual dimensions of the bearings (bore diameter, outer diameter, inner ring width, outer ring width) and the target value for these dimensions. Rotational accuracy, or runout, measures the degree of eccentricity of a bearing, and can be measured for side, axial, or radial runout of the inner or outer ring. A higher level of radial runout, for example, means more vibration at higher speeds for that bearing.
The tolerances for each grade are found in JIS and ANSI/ABMA standards. Minebea’s products are based on JIS B 1514-1, -3, ANSI/ABMA Std. 12.2 and ANSI/ABMA Std. 20.

The symbols used in the specification are as follows.

Symbol

Dimensions

d

:

Nominal Bore Diameter

D

:

Nominal Outside Diameter

D1

:

Outer ring flange outside diameter, basic

B

:

Nominal Inner Ring Width

C

:

Nominal Outer Ring Width

r

:

Chamfer Dimension of Inner Ring or Outer Ring

Dimensional Differences

Δds

:

Dimensional difference of bore diameter

Δdmp

:

Dimensional difference of mean bore diameter in the plane

(Δdm)

:

Dimensional difference of mean bore diameter

ΔDs

:

Dimensional difference of outside diameter

ΔDmp

:

Dimensional difference of mean outside diameter in the plane

(ΔDm)

:

Dimensional difference of mean outside diameter

ΔBs

:

Dimensional difference of inner ring width

ΔCs

:

Dimensional difference of outer ring width

ΔD1s

:

Deviation of a single flange outside diameter

ΔC1s

:

Deviation of a single width of the outer ring flange

Limit Values of Chamfer/Radius Dimension

rs

:

Chamfer dimension of inner ring or outer ring

rs min

:

Minimum dimension limit of inner ring and outer ring chamfer

rs max

:

Maximum dimension limit of inner ring and outer ring chamfer

Inequality of Dimensions

VBs

:

Variation of inner ring width

VCs

:

Variation of outer ring width

VC1s

:

Variation of flanged width

Rotation Precision

Kia (Ki)

:

Radial runout of inner ring

Sia (Si)

:

Axial runout of inner ring

Sd (Sdi)

:

Side runout of inner ring
[runout of inner ring reference face with respect to the bore]

Kea (Ke)

:

Radial runout of outer ring

Sea (Se)

:

Axial runout of outer ring

SD (SD)

:

Side runout of outer ring
[variation of outside surface generatrix inclination with respect to the outer ring reference face]

SD1

:

[variation of outside surface generatrix inclination with respect to the outer ring flange back face]

Sea1

:

Axial runout of outer ring flange back face

Remark ( ) is defined by ANSI/ABMA.
Reference [ ] is the expression used in previous JIS.
Attention : Above is only for radial ball bearing.